1. Field of the Invention
The present invention relates to a rapid process for treating a substrate with a plasma, such as a film deposition process, an etching process and an ashing process. More particularly, the present invention relates to a rapid process for depositing a diamond-like carbon (hereinafter sometimes abbreviated as “DLC”) film having superior properties with respect to wear resistance, surface smoothness, insulating properties, hardness, and the like. The present invention also relates to an apparatus for fabricating, on a polymer substrate, a long-endurable magnetic recording medium suitable for mass production, and yet having high recording density. Accordingly, the application field of the present invention covers a wide area ranging from visual equipments to information apparatuses.
2. Prior Art
The application field of diamond-like carbon films is widely spreading these days because the films are as hard as, or even harder than, the conventionally known hard thin films of, for example, TiC, TiN, SiC, Si3N4, and Al2O3, and yet, the DLC films can be deposited at room temperature without the application of a heating process.
Recently, a plasma treatment is applied in a wide field of industry to not only a semiconductor process but also a surface of a metal, a fiber and a plastic. Main plasma treatments can be classified into a film formation, an etching and an ashing and the like. Physical vapor deposition (PVD) and chemical vapor deposition (CVD) are known as the film formation. Sputtering is the representative process in the field of PVD (physical vapor deposition), while plasma CVD is the typical one in the field of CVD (chemical vapor deposition). Contrary to CVD, the etching and the ashing are processes in which a substance is removed from a substrate surface by a chemical or physical action of active species activated by the plasma. The CVD is generally carried out in a heated atmosphere, and the etching and the ashing are carried out at room temperature.
A low temperature CVD process for forming a film at a low temperature is desired in variety of application fields of CVD in that more kinds of substrate materials can be used in the low temperature CVD process, and cost of the substrate can be reduced by employing the low temperature CVD process. In particular, CVD making use of a kinetic energy of an ion is used for carbon film. The carbon film is formed with the carbon film receiving bombardment by the ion. A bond having a large bond energy is then selectively formed to form a film of high hardness which is collectively called a diamond-like carbon (DLC). Substrate heating is not particularly necessary in the formation of the DLC film as apparent from an elementary process of the formation of the DLC film. Therefore, the DLC films are promising as a variety of protection films from the cost advantage of the DLC films.
A DLC film can be formed by sputtering, e.g. a reactive sputtering using graphite or SiC partially containing silicon as the target material in a mixed gas atmosphere of argon and hydrogen.
FIG. 1 shows schematically the inner structure of a practically used prior art apparatus.
In general, the carbon source material for use as the starting material in the case of forming DLC by CVD include a saturated hydrocarbon gas such as methane (CH4) as described in JP-B-61-53955 or JP-B-62-41476 (the term “JP-B-” as referred to herein signifies an “examined Japanese patent publication”) and others containing more carbon atoms per molecule, or an unsaturated hydrocarbon gas such as methylene (C2H4) and others containing more carbon atoms per molecule. Furthermore, the use of substances containing silicon as partial substituents, such as tetramethylsilane (TMS; (CH3)4Si) and tetraethylsilane (TES; (C2H5)4Si) is also studied.
However, with the prior art film deposition methods or processes using the commercially available conventional apparatuses, it is fundamentally difficult to obtain a DLC film at a high rate of film deposition while maintaining its properties as a protective film at a favorably high level. In other words, a film of superior quality can be obtained only at the expense of the high rate of film deposition. Thus, in depositing a film of sufficiently high quality, a film deposition rate which is practically feasible is approximately in the range of from 0.1 to 0.3 μm/min. Moreover, the conventional apparatuses and methods for film deposition fail to achieve a satisfactory level of dehydrogenation to sufficiently accelerate the formation of covalent bonds between carbon atoms during the deposition of the carbon film.
In addition, it has been difficult to generate and maintain a stable plasma in depositing a film over a large area using the above static methods in which the substrates are fixed. The thermal damage which the substrates suffer upon film deposition at high rate also remains as a problems yet to be solved.
Recently, a higher recording density is required for magnetic recording media. Accordingly, the conventional magnetic recording media such as audio and video tapes which have been fabricated by a coating process, i.e., a process which comprises coating a polymer substrate with a magnetic powder of, for example, γ-Fe2O3, CrO, or pure iron, using a binder and an abrasive material, are now being replaced by those having a stable metallic thin-film type magnetic layer obtained by depositing a magnetic metal such as iron (Fe), nickel (Ni), cobalt (Co), and chromium (Cr), using PVD processes (in a broader meaning) such as vacuum deposition, plating, ion plating, and sputtering. In this manner, a magnetic recording media having not only a higher recording density but also a superior coercive force and an improved electromagnetic conversion property can be obtained at a higher productivity.
Recently, the DLC films are also formed using CVD processes represented by a plasma-assisted CVD or any of the PVD processes enumerated above.
It is still difficult to obtain layered thin films having favorable interface characteristics and surface properties using any of the above processes while maintaining a high rate of film deposition, because of the problems such as those associated with the step of air exposure and the like, and the technically difficult ones concerning synchronizing the deposition of the magnetic film and the DLC film at such a high film deposition rate. It is therefore desired to develop a new process of film deposition.